The sharp-tongued consumer advocate and Harvard Law professor is struggling to connect with working-class swing voters, many of whom seem more comfortable with Brown and his middle-of-the-road, regular-guy persona. Her fierce criticism of Wall Street has sent some Democratic Bay State financial types scurrying into Brown’s camp, too.

It’s the tale of two Elizabeth Warrens: the conscience of the left for many conventioneers vs. the candidate in real danger of losing the Democrats’ best Senate pickup opportunity of the year. A top dog in North Carolina, an underdog in Massachusetts.

Her problems are part Brown and part her own. Warren’s portrayal of the freshman senator as a covert ideologue hasn’t stuck, thanks to his soft tone on cultural issues like abortion and gay rights, coupled with a well-executed, down-home ad campaign.

And her campaign message isn’t resonating with a good number of Democrats. She’s losing about a fifth of them to Brown, according to an Aug. 16-19 Public Policy Polling survey that had the senator up by 5 points. And more voters think she’s too liberal than believe he’s too conservative — by an 11 percent margin.

“On the Democratic side, we’re the victims of our own spin with Scott Brown. In 2009, we said, ‘You look, he’s going to be a mess, an ideologue, he’s going to be stupid.’ Well, he hasn’t been any of those things,” said Boston-based Democratic consultant Scott Ferson. “She should be 10 points up. It’s a problem.”

Bruce Percelay, a longtime Democratic donor and close friend of Sen. John Kerry, is making a rare trek across party lines to support Brown. Percelay plans to work for Kerry’s reelection in 2014 and has given tens of thousands of dollars to Reps. Ed Markey and Mike Capuano as well as the national Democratic Party. But earlier this year Percelay gave $3,250 to Brown.

“Elizabeth Warren is not someone who I can comfortably wrap my arms around,” he said. “Not everyone is willing to express it, but [Brown] is the perfect Massachusetts Republican. He’s socially moderate and fiscally conservative and not a strong ideologue. People are very comfortable with that.”

In an interview, he said he was unsettled by the controversy surrounding Warren’s claim to Cherokee heritage and her hot rhetoric on economic disparity.

“While she’s very quick to chastise the wealthy, a lot of her fundraising is coming from very wealthy people on the West Coast,” he said. “There’s a concern about how genuine she is. Conversely, Scott Brown is an extremely genuine person.”